Selective telephone signaling system.



0,11; NORTH. SELECTIVE TELEPHONE SIGNALING SYSTEM.

APPLICATION FILED 001. 11, 1907. 1,008,282.

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UNITED STATES PATENT OFFICE.

CHARLES H. NORTH, OF CLEVELAND, OHIO, ASSIGNOR TO THE NORTH ELECTRICCOM- PANY, OF CLEVELAND, OHIO, A CORPORATION OF OHIO.

Specification of Letters Patent.

Application filed October 11, 1907. Serial No. 396,933.

To all whom it may concern:

Be it known that I, CHARLES H. NORTH, a citizen of the United States ofAmerica,

and a resident of Cleveland, in the county" of Cuyahoga and State ofOhio, have invented certain new and useful Improvements in SelectiveTelephone Signaling Systems, of which the following is a specification.4

hIy invention relates to a selective telephone-signaling system,affording for telephone exchanges an improved method of selectivesignaling, and has for its object the modification of selectivesignaling methods of the prior art, which shall be an advance inefliciency and eliminate false signals.

More particularly, my invention is ap plicable to telephone systems,wherein selective calling or signaling of a plurality of subscribersupon a given line is required, and my invention has been perfected withthis single end in view, whereby signaling currents are impressed uponthe line alternatively, which shall avoid the more or less activetendency observed in previous signaling systems to actuate two or moreof the selective calling appliances.

Until a compa 'atively recent date, it has been deemed commerciallypracticable to actuate signaling systems known as harmonicringingsystems, by means only of generator currents, which are respectively instep or tune with the signaling appliances used upon the multiple partylines. These currents, by reason of the fact that a single generatoroutfit was almost universally use(; in practice, operating at asubstantially fixed rate of speed, presented in frequency ofalternations, multiples of 2, 4, 6 and 8,' corresponding to therespective brushes of the dynamo. In consequence, there existed acoincidence in the electromagnetic impulses, which constantly tended tointerfere with the successful working of the system, and produced falsesignals, particularly for any extended or intermittent period ofsignaling or ringing. Prior to my application of the, principles ofnon-coinciding currents to selective signaling, I believe that theundesirable feature just alluded to,

had never been theoretically or practically overcome.

Although I do not deem my invention restricted to particular apparatus,it may most readily be practiced by the employment of interruptershaving definite rates of speed, in association with a source of directcurrent, but commutator devices, one of which I shall briefly advert to,may also be resorted to for practicing my invention, as herein describedand claimed.

Before explaining the means for practicing my invention, I may state, ina preliminary way, that the system of telephone signaling herein setforth, is one wherein the signaling currents adapted to beimpressed uponthe party line, are of such frequencies that they are non-coinciding in'efl'ect upon the several translating devices or ringers. In the simplefour-party line system, set forth for the exemplification of myimprovement, the current frequencies are multiples of '5, 7, 9 and 11,whose respective effects, I shall best be able to explain in connectionwith diagrammatic representations plotted to indicate the differentcurrents throughout their periods of noncoincidence, and compare themwith a diagram similarly plotted to represent the commercial four-partysignalingcurrents known to the prior art.

In said drawings, Figure I, represents a telephone system equipped withinterrupters and signaling bells assumed to be respectively tuned inaccordance with my im provement. Fig. II is a cross-sectional view of acommutator device; and Fig. III is a viewin side elevation of saidmultiple commutator, which represents other means for applyingnon-coinciding currents to a tele- Patented Nov. 7, 1911.

phone signaling system. Fig. IV is 3. diag'ammatic representation of theelectromagnetic effect of the four partially coinciding signalingcurrents of the prior art,

and Fig. V is a similar diagram of the the theoretical sine-wave, whichthe signaling currents approach, but I have employed. straight linesmeeting at angles instead of such curves, for making more apparent thepeak, or eii'ective magnetic variation of the respective alternatingcurrents ct \dill ercnt frequencies. These same diagrams may be taken,as well to indicate the respective relations between the preferredalternating currents employed in practicing my invention, but thisspecification may be made a little more direct and clear, by alluding tothe diagrams as representative of the magnetic ettiect ant. relationsresultant from said currents. Fig. V1 is an enlarged detailed diagram ofan interrupter-device.

'lhroughout the several figures of the drawings, 1 have employed thesame character oi rt-zfereuce to indicate similar parts, orcorresponding diagrammatic representations.

As stated, the alternating currents for selective singnaling, may bearbitrarily varied, so long as substantially the 1101 harmonic ordiscord relation exists between the respective currents. Thus, forfive-party selection, the cycles per second may best range between 30and 78, being multiples of the odd numbers from 5 to 13 inclusive.

Fig. 1 representing the preferred means for practicing my invention,will be explained in more detail as it embodies novel features inaddition to those herein claimed. in said. figure are shown four sets ofin terrupters, which are so adjusted with respect to each other as toimpress alternating currents when' respectively connected to line, whichhave frequencies representing substantially the multiples of live,seven, nine and eleven; these'iour being the simplest combination forpractically operating selective signaling systems, In this instance, wemay further assume that the common multiple is six, which I have foundmost desirable for practical purposes. Accordingly, the respectiveintt-irrupters a, a, 0i and a-'* will. be so constructed and justifiedas resppctively to impress upon the line alter nating currents ofthirty, forty-two, fiftyfour and sixtysix alternations per second.

Explaining first the structural features of the interrupter, it will beseen that-the vibrating member or reed a, equipped withv a variableweight a", is designed, undrr. the influence of laterally positionedelectromagnates bb, alternatively to engage the contact springs c 0thereof. These electromagnets each comprise a high and low re sistancecoil 17 b shunting each other and terminating respectively in thecontact spring 0 c.

In the preferred embodiment of my invention, the source of current, asbattery B, has one of its poles connected directly with the tongue orvibrating member 'a of the while the other pole of the batinterrupter,tery is connected directly with the high their respective excitationsgenerate poles of "like sign in each of the magnet cores. The

reed or tongue a preferably is of steel and is polarized, more readilyto respond to, the

about the contact springs 0' 0 and their respective associated windingsI) b is the condenser e.

As shown in the diagram, Fi 1, the secondary (Z of each converter d, isconnected through a resistance lamp cl? with the corresponding contactse, 6 6 e of an operators selective key, controlling the flow of currentto the calling plug p of the cord .circuit, which is shown inserted inthe pack p of a four-party selective telephone line. Each station uponsaid line, connectedbetween conductors l, 2, is designated by asignaling bell f, P, f, y with its'associated condenser the ordinarysub-station apparatus being omitted as unnecessary. Moreover, thecustomary cord circuit and line signaling apparatus is conventionallyindicated in the. diagram, sufiiciently to illustrate the principalapplication ot the invention, but I do not consider that these featuresrequire explanation herein.

Each of the interrupters a, a a a is connected in circuit precisely asexplained above, employing converters (1 whereby to transmit current tothe signaling circuit, but the reeds or vibrating member of saidintcrrupters and their weights, are respectively made stiffer andlighter for the high frequencies, and more flexible and heavier for thelow frequencies. sired number of these adjusted interrupters may beemployed. \Vith respect to the windings upon the electro-magnetslb b ofthese interrupters, vided with more turns upon the high frequencyinterrupter-s than upon the low, while the co-a'cting shunt coils areprovided with fewer turns upon the coils of the high freterrupters.Preferably this is found to be desirable in practice, for the reaso'uthat with the stitl'er reeds and higher rates of vibration, more workmust be done by the high 'lrcqucncy electro-magnets, and as an ex am leof a i )roximatel the referred numl l P excitation of the magnet coils.Bridgedljractically any de-- I quency interrupters, than upon thecorrespondmg windings of the low frequency 1nthe series coils, are provCurrent then flows through windings m i will be. well understood. causesaltermiting her of turns for a tour-party line employing twenty-fourvolts on the primaries, I may say that the highest frequency interrupterwill have 100 turns upon its series coil, and

6500 turns upon the shunt coil, while the lowest frequency interrupterwill have 4.0 3

turns upon the series coil, and 12,500 turns upon its shunt coil; thewindings upon the other interrupters bein intermediate of these two. Ihave preterably wound the secondaries to generate 160 volts in the.naling circuit, and this I findjis transmitted with relatively smalldrop in voltage, even to the most distant stations. This is because ofthe fact that the series coils are energized by the full flow of currentand'impart a more powerful vibratory movement to the contact member (1,thereby insuring a longer closure of the respective magnet circuits,

tending to secure approximate magnetic saturation ot' the iron body ofthe converter, and thereby transmitting the maximum voltage from thesecondary winding. This operation probably will be better understood bymaking further reference to the diagram, Fig. I, and assuming that oneof the stations is to be rung, as station 7'. Assuming too.

that the line has been tested, and the calling plug inserted in theproper jack, the operator will actuate her selective key, closingtogether the contact a. All of the interrupters are in operation underthe impulse of their respective shunt windings, but immediately upon theclosure of the contacts a, the impedence of the converter connected withinterrupter a will at once be reduced, thereby permitting the flow ofexciting current through the divided primary windings (2'. Current maybe traced from the upper pole of the battery, through the connnonconductor to the. vibrating member a, contact 0, series winding 7/, theright hand portion of the primary winding 1?. and conductor 3 to thelower pole of the battery. The vibratory member is augmented in itsmotion and is actuated by the series winding out of engagement withcontact and into engagement with contact 0, thereby opening circuit withcontact and its connected windings, and closing the circuit with contact4- and the connected windings upon the lc'lt.

thereof, and theleft hand coil of the primary winding (Z' upon theconverter. This, as

the sleeve of the plug. the contacts of the operators key, and contacts(1' (assumed to be closed), and conductor 5 to the right hand 1 side ofthe secondary windings. The bell f, will, ot course, respond to thiscurrent ot proper trtapicncy, while the remaining bells upon the linecircuit will fail to be actuated, as will be well understood by those.conl versant with the art.

In practice. each of the interrupters. upon installation is connected incircuit as shown. The adjusting screws 1/ are separated to such anextcnt that neither of the contact springs c c is in engagement with thevibratory member (I. ()ne of these screws as 5/ is then turned until thecontact spring c is brought into engagement with the contact of thevibratory member. whereupon it will start under the impulse of but asingle magnet. This screw then turned back slightly. say to the extentof one quarter turn, aml the opposing screw y is'thcn turned until tlncontact I" similarly is brought into engagemcut with the contact of thevibrating member, whereupon this screw is also set in its ad: justedposition and the interrupter device will continue normally undertheimpulse of its shunt windings. It will be scen, however, that with aslight bias, the vibrating member may be actuated by a singleelectromagnct, but preterably l employ the arrangemcnt herein set forth.The mechanical features thereof are explained at greater length andclaimed in the application of John F. Engle, tiled June 12th, 1907,Serial No. 378,549.

The respective sets of brushes j engage the commutator segments, and thesame are arcs provided in their su 'iporting standards From thesebrushes, the respective alternating currents are taken off in lieu ofthe. 1 several transformer currents of Fig. I, to which they maycorrespond in non-harmonic relation. are respectively provided with anincreasing number of segments, which are so coupled or connectedtogether between their terminals m by cross wires in disposed.therebetween, as to secure substantially non-harnating currents. Thisrelation is also ads i ustable or alter-able in .large measure by ingsupported between the bearings 71. 71

imlividually adjustable within the slotted' The several cominutators7"y'*' monic relation bet ween the respective altcr- Instead of theinterrtmters, I may em-- 'em ploycd moving the respective brushes withintheir arced paths. The relative number of cycles per second, will, ofcourse, be dependent upon the speed at which the multiple comn'mtatordevice is rotated, and since substantially constant speed is requirethldo not recommend or rely upon the mechanical features just aboveexplained in practicing my invention. Connnutators or rotary contacts 2'2', are merely slip-rings engaging the main brushes, and are suitablyconnected up with the multiple COllllIlllttll'OL contacts.

Iii-order to present my invention graphically and more clearly, I haveplotted the diac' arms of Figs. IV and V, the former of which isrepresentative of the standard four-party frequencies of 16%, and 66%cycles per second. The latter is representa tive of the currentfrequencies, preferably in practicing my invention. It

will be appreciated, that as between the frequencies of 33,, and 50cycles per second, there exists the relation of a musical fifth, whilebetween all of these current-cycles, excepting only the third, or 50,there exists the octave rcla on, hence the propriety of terming thesystems of the art harmonic signaling systems.. The most casualcomparison of these two figures, IV and V, demonstrates the vastsuperiority of the nonharmonic currents for selective signaling. Fig.IV, shows the coincidence of the four harmonicalternating currents,which occurs e: ch .06 of a second, as opposed to the nonharmoniccurrents which coincide only six times each second, above the zero line.By reason of the necessary coincidence of the harmonic currents, falsesignals are constantly liable to occur, particularly as between thecurrents havingrespectively 16%,- and 50 cycles per second, which are inco-' incidence during two-thirds of the time.

' Another frequently observed source of 1nterferences, is thecoincidence likely 'to 00- our when the armatures of the bells,responsave to currents having cycles per second,

, are slightly off center, thereby materially employcd upon partyphasizing-the disturbing coii'icidencc during half of the swing of saidarmature. More than this, bells responsive to the lowest frequency, areopen to the serious-objection of being. responsive to currentstransmitted by the ordinary hand generator, frequently em- Whenfrequencies of substantially 30 cycles per second, or higher, areemployed, however, it is impossible'to ring any of the selective bellsbymeans of a hand generator, for. the reason that it is impossible to turnthe generator fast enough -'nanually. it; will he iobservcd, that in theneferred frequcncies, employed in practicing my in vcntion, the lowest.frequency corresponds approximately with the second frequency effects ofthese currents are employed in the prior art, and the objection lastalluded to, is at once eliminated. Considering Fig. V, it is seen thatthe magnetic non-coinciding above the zero line, throughout therelatively long period of one-sixth of a second, and because of thediversity of these current effects, false signals are renderedimpossible with the use of non-harmonic currents. To recapitulate, incomparison" t' these preferred methods of selective sign-aiing, itwillbe noted as stated above that the frequencies employed in thenon-harmonic system bear the relation of discords to each other, whereasthe frequencies employed in the bar nonic system bear, as the name wouldindicate, the relation of harmonics to each other. For example, reducedto their lowest terms it will be observed that the HOD-lltll'illOlllCfrequencies bear the relation to cach other of 7, 9, and 11, while theharmonic frequencies bear the relation to each other of 1, 9, 3, and 4.

One of the chief ditliculties encountered in the operation of theharmonic system has been due to the liability to cross ring. Thistendency has been particularly noticeable between the 16% cycle and the50 cycle ringers. although the other frequencies have not been entirelyfree from the same charactcrof trouble. Upon analyzing; the waves of thearious cycles or frequencies the reason for this interference is quiteobvious. The laws governing the vibration of nonharmonic and harmonicringers, vibrators or polc changers are the same as those gov erningjthevibration of musical reeds or springs. lt-iswell known that if a reed ofany pitch or frequency is vibrated, all other reeds in close proximityto it, or which are subjected to the same force which actuates the reedin question, in synchronism or harmony with the reed vibrated arealsocaused to vibrate. l/Vhen one vibrating reed. in close proximity toanother causes the latter to vibrate, it is known as sympatheticvibration.

Sympathetic vil'n-ation is most pro nounced between two synchronousreeds, or reeds vibrating in the same period and as between these tworeeds perfect harmony exists. .Next in matter of harmony is the octave,as where one reed vibrates twice as, rapidly as the other. Next followsthe fifth with a ratio of two to three. It will boobscrvcd by referenceto the ordinary harmonic frequencies that we have the ratio both ofoctaves and fifths between the sovcral frequencies, and when a currentof any -iven t'rta'ptcncy is impressed on the line, it naturally followsthat any ringer tuned-in synchronism with the ringing current, willrespond. This is as it should he, as this is the principle upon whichthe system is and which are either are of uniform capacity.

based, but it also follows that any ringer. in l harmony with theimpressed current will also respond to a greater or less degree.dependent upon the ratio of coincidence. This latter application of theprinciples involved is the real root of the cross-ringing troubleexperienced in harmonic systems. and it is seen that making one reed ofsuch asystem in harmony with another reed of a different frequency isreally a violation ofv the very principle upon which the system isbased, and upon which it depends for its margin of safety.

In harmonic systems the margins are so small as to make it necessary towind the ringers to different resistances. The 16 cycle ringer is woundto 2500 ohms; the 33,, cycle from 500 to 2250 ohms, and the 50 cycleand, 66% cycle ringers are usually wound to 500 ohms each, although themar gin of safety could be made somewhat wider by aarying these windingssomewhat from those usually employed. In the herein describednon-harmonie system, all ringers may he wound to the uniform resistanceof 1000 ohms, and are in all respects precisely alike with the.exception of the weight on the armature. 'Ihearmatures for the variousfrequencies preferably are interchangeable. and if it should be desiredto change a ringer from one frequency to another the only thing which itis necessary to do is to remove the armature from the ringer 1 andreplace it by an arn'iature properly adjusted for the frequency upon,which'the-ringer is to be used. This makes it unnecessary to keep astock of ringers for the different frequencies on hand, but instead asupply of these interchangeable armatures alone is required. The marginof safety in the harmonic systcn'i is so slight as to. make extremelyaccurate adjustment of the ringers necessary. and it is also essentialthat the condensers used in series with the ringers Vvith thenonharn'ionic system having much wider mar gins, ti extreme care. inadjustment and in the sleetion of condensers is not required. in thecase of the foregoing system it will he noticed as stated above, thatthe frecords to each other, and by using (these fre quencies the elementof sympathetic vibrationand consequent cross-ringing is eliminated andthe working margin greatly amplified.

Metallic circuit lines affording the best and mostapproved method ofpracticing my invention, have been considered alone herein, but it willbe appreciated that the number of possible party line stations may bedoubled with a given number of selective signaling currents. merely byresorting to the expedient of ringing over either limb of the metallicline to ground, in a manner well known in the art.

In the foregoing. I have endeavored to set forth the preferred practicaldetails, and the theories of operation as understood by me, but I do notwish this to be interpreted as necessarily limiting my invention to suchdetailsfand accordingly claim the following:

1. In a system of the class (lQSCIibGththQ combination with a centraltelephone exchange, of a plurality of multiple-station telephone-linesconnected therewith; each of said lines being equipped withselective-signaling apparatus at the. different stations respectivelytuned to respond to currents of different inharmonic frequencies, andthe said telephone exchange being equipped with calling-apparatusproducing currents of corresponding inharrnonic frequencies,substa'ntially as set forth.

2. In a system of the class described, the combination with a telephoneexchange equipped with signaling-apparatus produc ing currentsapproximately of 30, 4:2 and 54 cycles per second, of a plurality ofmultiplestation telephone-lines connected with said exchange; each ofsaid lines being equipped with selective-signaling apparatus at thedifferent stat-ions. respectively tuned to respond -to currents of theseinharmonic frequencies,

substantially as set forth.

3. In a telephone exchange system, the combination with central-officeequipment, including sources'of alternating signaling currents Whosefrequencies are substantially multiples of five, seven. and nine, ofamultiple-station telephone-line, including at carpi} station asignaling device respectively.

tunedto respond to currents of the different frequencies, substantiallyas set forth.

4:. In a telephone exchange system, the combination with central-ofliceequipment, including a source of current and associated converter andinterrupter devices adjusted to supply currents of diflerentnon-harmonic frequencies, and a multiple-station telephone-lineincluding at each station a. signaling-bell respectively tuned torespond to currents of the different frequencies, substantially as setforth.

5. The combination with a telephone switchboard, of sources of signalingcurrents adapted alternatively to be connected in circuit with a calledline; said currentsbeing of non-harmonic frequencies, a multiple-stationtelephone-line connected to said switchboard .and at each station asignaling-bell respectively tuned to respond to currents of distinctivefrequency, substantially as set forth.

6. In a telephone exchange system, the

combination with central-office equipment,

rupter devices adjusted to deliver currents of I Signed zit Cleveland,this tenth day of different n0n-lmr1n0nic frequencies, and a October, A.D. 1907, in the presence '01 two plurality of multiplestation telephonelines subscribing Witnesses.

extending to the central-office; and at each CHARLES H. NORTH. 5 stationa signaling bell tuned to respond to Witnesses:

currents of one of the n0n-harmonic fre- Jesse A. BUEL,

quencies, substantially as set forth. ALBERT LYNN LAWRENCE.

